Conventionally, in the manufacture of semiconductor devices, micro-processing by lithography using a photoresist has been carried out. The micro-processing is a processing method comprising forming a thin film of a photoresist on a semiconductor substrate such as a silicon wafer, irradiating actinic rays such as ultraviolet rays through a mask pattern on which a pattern for a semiconductor device is depicted, developing it to obtain a photoresist pattern, and etching the substrate using the photoresist pattern as a protective film, thereby forming fine unevenness corresponding to the pattern on the surface of the substrate. However, in recent progress in high integration of semiconductor devices, there has been a tendency that shorter wavelength actinic rays are being used, i.e., ArF excimer laser beam (193 nm) has been taking the place of KrF excimer laser beam (248 nm). Along with this change, influences of random reflection and standing wave of a substrate have become serious problems. Accordingly, it has been widely studied to provide an anti-reflective coating between the photoresist and the substrate (Bottom Anti-Reflective Coating, BARC) in order to resolve the problem. As the anti-reflective coating, from a viewpoint of easy of use, many considerations have been done on organic anti-reflective coatings made of a light absorbing substance and a polymer compound and the like. For example, mention may be made of the acrylic resin type anti-reflective coating having a hydroxyl group being a crosslinking reaction group and a light absorbing group in the same molecule and the novolak resin type anti-reflective coating having a hydroxyl group being a crosslinking reaction group and a light absorbing group in the same molecule (see, for example U.S. Pat. Nos. 5,919,599 and 5,693,691).
The physical properties desired for organic anti-reflective coating include high absorbance to light and radioactive rays, no intermixing with the photoresist layer (to be insoluble in photoresist solvents), no diffusion of low molecular substances from the anti-reflective coating into the topcoat photoresist upon baking under heating, and a higher dry etching rate than the photoresist (see, for example, Tom Lynch et al., “Properties and Performance of Near UV Reflectivity Control Layers”, US, in Advances in Resist Technology and Processing XI, Omkaram Nalamasu ed., Proceedings of SPIE, 1994, Vol. 2195, p. 225-229; G. Taylor et al., “Methacrylate Resist and Antireflective Coatings for 193 nm Lithography”, US, in Microlithography 1999: in Advances in Resist Technology and Processing XVI, Will Conley ed., Proceedings of SPIE, 1999, Vol. 3678, p. 174-185; and Jim D. Meador et al., “Recent Progress in 193 nm Antireflective Coatings, US, in Microlithography 1999: in Advances in Resist Technology and Processing XVI, Will Conley ed., Proceedings of SPIE, 1999, Vol. 3678, p. 800-809).
In recent years, in order to solve interconnection delay that has become clear with miniaturization in pattern rule of semiconductor devices, it has been considered to use copper as interconnect material, and to apply Dual Damascene process as interconnect forming method on the semiconductor device. And, in Dual Damascene process, via holes are formed and an anti-reflective coating is formed on a substrate having a high aspect ratio. Therefore, the anti-reflective coating for use in this process is required to have filling property by which holes can be filled without gap, flattening property by which a flat coating can be formed on the surface of substrate, and the like.
However, it is difficult to apply organic material for anti-reflective coating on a substrate having a high aspect ratio, and in recent years, material with particular emphasis on filling property or flattening property has been developed (see, for example JP 2000-294504 A, JP 2002-47430 A, JP 2002-190519 A and WO 02/05035 pamphlet).
In addition, in the production of devices such as semiconductors, in order to reduce poisoning effect of a photoresist layer induced by a dielectric layer, there is disclosed a method in which a barrier layer formed from a composition containing a crosslinkable polymer and the like is provided between the dielectric layer and the photoresist layer (see, for example JP 2002-128847 A).
As mentioned above, in the recent manufacture of semiconductor devices, in order to attain several effects represented by anti-reflective effect, it comes to provide an organic underlayer coating formed from a composition containing an organic compound between a semiconductor substrate and a photoresist layer, that is, as an underlayer of the photoresist.
Such an underlayer coating is required to have a high dry etching rate compared with the photoresist. The processing of semiconductor substrates is carried out by dry etching by using as a protective coating the photoresist on which a pattern is formed. In this process, prior to the substrate, an underlayer coating is removed by dry etching by using as a protective coating the photoresist. Thus, film thickness of the photoresist is reduced also in the removal of the underlayer coating. In addition, if it takes a long time to remove the underlayer coating, the reduced amount of the photoresist becomes large, and this causes a problem that the photoresist cannot maintain a film thickness required for the processing of substrates. Particularly, in recent years, in order to prevent collapse of photoresists with miniaturization in line-width of photoresist pattern, it comes to be desired to reduce the thickness of photoresists. Therefore, an underlayer coating removable for a short time, that is, an underlayer coating having a high dry etching rate comes to be required than ever before.
Taking the above-mentioned present status into account, the present inventors have eagerly studied, and as a result of it, found that when as an underlayer coating, a coating having pores, that is, a porous underlayer coating is adopted, the removal rate thereof by dry etching can be increased, and they completed the present invention.
That is, an object of the present invention is to provide a method for forming photoresist pattern for use in manufacture of semiconductor device, including a step of forming a porous underlayer coating having a high dry etching rate on a semiconductor substrate.
In addition, another object of the present invention is to provide an underlayer coating forming composition used for forming a porous underlayer coating, and further to provide a porous underlayer coating formed from the composition, and to a method for forming a porous underlayer coating by using the composition.